The invention concerns a rotary slide set for a hydraulic steering arrangement with an outer rotary slide and an inner rotary slide arranged in the outer rotary slide, and having in its surface tank grooves, which are, at least in predetermined rotary positions, connected with a low pressure connection, and at least one through-opening in its wall, each overlapping, at least partly, a tank groove.
Such a rotary slide set is known from U.S. Pat. No. 4,804,016. Such a rotary slide set is, for example, used in a steering arrangement for a hydraulic steering. The inner rotary slide is turned by a steering member, for example, a steering wheel shaft. The turning occurs firstly in relation to a housing and secondly also in relation to the outer rotary slide. In a way known per se, and described in detail in U.S. Pat. No. 4,804,016, this mutual turning results in the release or the closing of flow paths, leading from a pump connection to a first working connection and from a second working connection to a tank connection or a tank pressure connection. The hydraulic fluid flowing out of the first working connection, or a share proportional to it, is led through a measuring motor, which turns the outer rotary slide via a cardan shaft. The cardan shaft is arranged in the inner rotary slide and connected with the outer rotary slide via two pins arranged diagonally opposite to each other, which are led through the through-openings in the wall of the inner rotary slide.
Hydraulic steering arrangements of this kind have proved their value. However, often the problem occurs in this connection that the inner rotary slide gets jammed in the outer rotary slide, or the outer rotary slide gets jammed in the housing. To the operator, for example the driver of a vehicle equipped with such a steering arrangement, this means an increased force for the activation of the steering wheel, which feels unpleasant. Additionally, dangerous situations may occur, when the rotary slides get jammed in relation to each other or in the housing, as then the xe2x80x9ccorrectxe2x80x9d fluid control is no longer guaranteed. For this reason, a number of proposals have already appeared to avoid such jamming. Such a proposal is described in U.S. Pat. No. 4,804,016.
Another proposal appears from U.S. Pat. No. 5,165,447, in which it is attempted to maintain the same pressure inside and outside the inner slide, at least in certain areas.
The invention is based on the task of providing an additional opportunity of avoiding a jamming.
With a rotary slide set as mentioned in the introduction, this task is solved in that at the remaining tank grooves surface recesses have been made to serve as balancing areas.
This is based on the following consideration: The throughbore, which can also be called xe2x80x9cpin holexe2x80x9d, is connected with a tank groove. Accordingly, the tank pressure rules in the pin hole, or generally the lowest pressure in the steering arrangement. In the remaining tank grooves, the area, in which the tank pressure rules, is smaller. Thus, outside the tank groove a different pressure can build up, which is larger than the tank pressure. This involves the risk that the inner rotary slide is deformed to a shape deviating from the circular shape, for example an oval or elliptic shape. As the inner rotary slide and the outer rotary slide are made with relatively narrow fitting in relation to each other, even small deformations will be sufficient to cause a jamming. When, now, it is provided that the conditions at the tank groove with the pin hole and at the remaining tank grooves are similar to each other, it can be ensured that the pressure on the inner rotary slide in the circumferential direction is accordingly point-symmetrically distributed, so that the risk of a deformation of the inner slide remains relatively small. In other words, the rotary slide is equally loaded from all sides, and not only in the area of the pin hole. The pin hole is also xe2x80x9ccopiedxe2x80x9d to the remaining tank grooves, so that a relatively good symmetry occurs with regard to the hydraulic load.
Preferably, the balancing areas have the same size as the effective surface of the through-opening. The more equal the conditions are, the better the inner slide is in balance, and the smaller is the risk of a deformation.
Preferably, the balancing areas are arranged in relation to the tank grooves exactly like the through-opening. Also here, a substantially identical transmission of the conditions will contribute to an improvement of the balance situation at the inner rotary slide.
In a particularly preferred embodiment it is provided that the inner rotary slide has a fitting area and an ease-off area, the through-opening passing through a boundary between the fitting area and the ease-off area and the balancing areas extending from the ease-off area into the fitting area. In fact, a tight fit between the inner rotary slide and the outer rotary slide is only required, where fluid flows have to be sealed against hydraulic fluid under pressure. For hydraulic fluid returning to the tank, such tight fits are no longer required. Usually, hydraulic fluid returning to the tank has such a low pressure that significant leakages are not to be feared or at least harmless. Therefore, an ease-off area may be provided, in which the diameter of the inner rotary slide is slightly reduced in relation to the diameter of the fitting area. At least, such an embodiment prevents a jamming between the inner rotary slide and the outer rotary slide in this area. When now the through-opening or the pin hole is provided on the boundary between the ease-off area and the fitting area, then only a share of the fitting area is xe2x80x9cpressure releasedxe2x80x9d. Accordingly, it is sufficient to extend the balancing areas, which correspond to the cross section of the pin hole, into the fitting area, that is, to copy the part of the contour of the pin hole, which is placed in the fitting area, to the remaining tank grooves, so that in a similar way the ease-off area can extend into the fitting area.
It is particularly preferred that in the fitting area the balancing areas have the same contour as the through-opening. Thus, a simple production guide is obtained for the inner rotary slide, and a correspondingly good hydraulic balance.
Preferably, at least three tank grooves are arranged in the circumferential direction. The pressure release, which corresponds to that of the pin hole, thus distributes evenly in the circumferential direction on three areas. The risk that deformations still occur is relatively small.
Preferably, two through-openings arranged opposite of each other are provided. Thus, the torque transmission from the cardan shaft to the outer rotary slide is improved.